(function(){

	 function dateStart()   
   {   
       //月份对应天数
       MonHead = [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31];   
    
       //给年下拉框赋内容   
       var y  = new Date().getFullYear();   
       for (var i = (y-50); i < (y+50); i++) //以今年为准，前50年，后50年   
           document.date.year.options.add(new Option(" "+ i +" 年", i));   
    
       //给月下拉框赋内容   
       for (var i = 1; i < 13; i++)   
           document.date.month.options.add(new Option(" " + i + " 月", i));
   
       document.date.year.value = y;   
       document.date.month.value = new Date().getMonth() + 1;   
       var n = MonHead[new Date().getMonth()];   
       if (  new Date().getMonth() ==1 && IsPinYear(yearvalue)  ) 
           n++;   
       writeDay(n); //赋日期下拉框   
       document.date.day.value = new Date().getDate();   
   } 
  
   if(document.attachEvent)   
       window.attachEvent("onload", dateStart);   
   else   
       window.addEventListener('load', dateStart, false);   
 
   function selectYear(str) //年发生变化时日期发生变化(主要是判断闰平年)   
   {   
       var monthvalue = document.date.month.options[document.date.month.selectedIndex].value;   
       if (monthvalue == "")
       {
           var e = document.date.day;
           optionsClear(e);
           return;
       }   
       var n = MonHead[monthvalue - 1];   
       if (  monthvalue ==2 && IsPinYear(str)  ) 
           n++;   
       writeDay(n);   
   }   
 
   function selectMonth(str)   //月发生变化时日期联动   
   {   
        var yearvalue = document.date.year.options[document.date.year.selectedIndex].value;   
        if (yearvalue == "")
        { 
            var e = document.date.day; 
            optionsClear(e);
            return;
        }   
        var n = MonHead[str - 1];   
        if (  str ==2 && IsPinYear(yearvalue)  ) 
            n++;   
            writeDay(n);  
        }   
 
   function writeDay(n)   //据条件写日期的下拉框   
   {   
       var e = document.date.day; optionsClear(e);   
       for (var i=1; i<(n+1); i++)   
           e.options.add(new Option(" "+ i + " 日", i));   
   }   
 
   function IsPinYear(year)//判断是否闰平年   
   {     
       return(  0 == year%4 && ( year%100 !=0 || year%400 == 0 )  );
   }
 
   function optionsClear(e) 
   { 
       e.options.length = 1; 
   }
})();